Heat-meltable fluoropolymers, such as tetrafluoroethylene-perfluoro(alkylvinylether) copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and tetrafluoroethylene-ethylene copolymer (ETFE) are used for the holding jigs and tube materials for the chemical liquid supply line in semiconductor manufacturing equipment because of their excellent heat resistance, chemical resistance, non-stickiness and other properties. However, the tubes made of these resins have to be replaced periodically owing to such problems as the contamination of the peripheral devices and environmental pollution due to the permeation of the chemical liquid. For this reason, there is a demand for materials showing lower chemical liquid permeability. Furthermore, when these resins are used for the heat exchanger tubes in an alkali tank, the tubes show low thermal conductivity, and therefore there is also a demand for materials exhibiting higher thermal conductivity.
For the purpose of solving these problems, there is a demand for a resin composition showing higher performance in various fields. For this purpose, improvements of the mechanical strength, chemical or gas permeability, thermal conductivity, etc., for example, by dispersing a filler in the resin are proposed. Especially, many attempts are made to use the technique of dispersing or cleaving a layered-compound in a polymer material or intercalating a polymer compound between the laminas of a layered-compound to improve the mechanical properties and chemical liquid or gas permeability of such resin, or the technique of dispersing a carbon compound in a polymer material to improve thermal conductivity.
For example, Japanese Patent Publication 2000-190431 describes a multi-layer laminate whose gas or chemical liquid permeability is lowered by melt-mixing a scale-like filler and a fluoropolymer and by laminating. Furthermore, Japanese Patent Publication HEI 2-10226 describes a method in which a layered clay mineral used for a filler is organically-modified, a monomer is inserted into the space between the laminas of this layered-compound where interlaminar distance is increased by organic-modification, and then the layered-compound is dispersed on nano scale by utilizing polymerization energy released during the polymerization of the aforesaid monomer. However, the aforesaid polymerization method cannot be said to be economical because although the polymerization method allows the filler to be dispersed efficiently, it requires polymerization equipment, entailing high cost. Besides, since the monomer that is inserted between the laminas of the aforesaid layered clay mineral will not stay stably between the laminas, a gas monomer is not preferable, and the choice of the monomer is limited to a liquid monomer.
As a method for improving these problems with the polymerization method, each of Japanese Patent Publication HEI 7-47644 and Japanese Patent Publication HEI 7-70357 describes a method in which a layered clay mineral is organized with organic cations in advance, the layered clay mineral is caused to be infinite-swolled by use of an organic solvent, and then the clay mineral is caused to come into contact with a melted resin liquid so that it is dispersed in the resin on nano scale. However, such method essentially requires the use of a large amount of an organic solvent in causing a layered clay mineral to be swelled, but a fluoropolymer has the problem of extremely low compatibility with an organic solvent. On top of that, the infinite-swollen layered-compound by use of the aforesaid organic solvent also has the problem of returning to a swollen state from such infinite-swollen state as part of the organic solvent will evaporate at the temperature of extrusion of the fluoropolymer in such process of coming into contact with the melted resin.
Furthermore, as a means for improving the problems with the layered-compound using such organic solvent, there is a method, for example, in which an organically modified layered clay mineral and resin pellets are melt-mixed by shear stress directly in an extruder so that such organically modified layered clay mineral is dispersed in the resin matrix. In connection with this, there is a report on the physical properties of a composite mixture in which such layered-compound is dispersed by changing the types (single-screw and twin-screw) of the extruder and the mixing method (co-rotating, counter-rotating, intermeshing and non-intermeshing) of a twin-screw extruder, among other conditions. However, there was no significant improvement reported in the mechanical properties of a composite mixture in which the layered clay mineral was dispersed which had been organized to some extent by melting and mixing the layered clay mineral by means of a twin-screw extruder of the non-intermeshing type with the result that the inter-layer distance was increased (Plastic Engineering, P56, 2001).